This invention relates to power supply systems including a rechargeable battery, and more particularly, to a vehicle battery system including a main battery and an auxiliary battery and which provides a battery back-up function and opportunity charging of the auxiliary battery.
Vehicle battery systems including a main battery and a reserve battery are known. One such battery system disclosed in U.S. Pat. No. 5,002,840 includes a main battery and a reserve battery disposed within a common housing. A unidirectional charging circuit connects the reserve battery in parallel with the main battery, permitting charging current to flow into the reserve battery, but preventing drain of the reserve battery during normal vehicle operation. When the main battery output is insufficient to start a vehicle, a switch is manually operated to connect the reserve battery in parallel with the main battery. The reserve battery provides sufficient power for the operator to start the vehicle. When the vehicle has been started, the switch is operated to disconnect the reserve battery from the starter circuit. The main battery is charged in a conventional manner and the reserve battery is recharged at a lower rate through the unidirectional current circuit.
An improved dual battery system is disclosed in U.S. Pat. No. 5,204,610 entitled Long Lived Dual Battery With Automatic Latching Switch, which issued on Apr. 20, 1993. This system, which is described with reference to the electrical system of a motor vehicle, includes a circuit for monitoring a parameter, such as primary battery voltage, of the main battery and for causing the reserve battery to be connected into the starting circuit when the primary battery voltage drops below a predetermined threshold value. In one embodiment of the system, the switching circuit is effective to connect the reserve battery into the starting circuit only when the primary battery voltage is below the preselected value prior to operating the ignition key to energize the starting circuit. In another embodiment, the switching circuit disconnects the reserve battery from the starting circuit when the ignition key is operated to the "ignition off" position, or after a preselected interval of time. The switching circuit includes a timing circuit to prevent the reserve battery from being discharged for an inordinately long period of time and to allow for its recharge. This arrangement obviates the need for operator intervention to manually operate a switch to activate the reserve battery system when required and to deactivate the reserve battery system when reserve power is no longer required.
A further consideration is the increasing demand on battery power for energizing vehicle accessories such as electrically heated catalytic converters, vehicle battery heaters, electric heaters for vehicle seats, windshield defrosters, and other non-critical accessories. Accessories of this type must be energized prior to or during the starting of the vehicle, this resulting in a significant drain on the main battery during the engine starting cycle, when maximum power is required.
For example, most gasoline-fueled vehicles in use today include a catalytic converter for reducing pollution. The catalytic converter may be heated electrically to optimize its performance. Power for heating the catalytic converter is obtained from the vehicle battery. Because the catalytic converter must be heated prior to or at the time of starting of the vehicle engine, a substantial electrical load is placed on the vehicle battery prior to, during or immediately after starting of the engine.
It is known that batteries charge less effectively and have reduced available power at lower temperatures. Consequently, various arrangements have been proposed for assuring a given battery temperature prior to starting of the vehicle. Most of the systems employ a heating element powered from the vehicle battery. Arrangements have been proposed whereby the battery is heated only when the battery voltage of the battery reaches a certain predetermined value which depends upon the battery's state of charge and on battery temperature. An example of a battery heating system employing a charge management strategy is disclosed in U.S. Pat. No. 5,055,656. These charge management strategies result in a greater average battery state of charge through increased charge acceptance and improved discharge performance resulting from increasing the temperature of the battery.